Ambient mass spectrometry has been defined practically as any method of ionization allowing for the sampling of an analyte from a surface or ambient atmosphere without advance sample preparation, occurring at ambient pressure. There are a number of somewhat distinct methodologies for ambient mass spectrometry. Several, like desorption electrospray ionization (DESI), (See Cooks, R. G.; Ouyang, Z.; Takats, Z.; Wiseman, J. M. Science 2006, 311, 1566-1570.) are derived primarily from electrospray ionization (ESI). Others utilize laser desorption to volatilize the sample, including ambient pressure matrix assisted laser desorption ionization (AP-MALDI). (See Laiko, V. V.; Baldwin, M. A.; Burlingame, A. L. Anal. Chem. 2000, 72, 652-657, and Laiko, V. V; Moyer, S. C.; Cotter, R. J. Anal. Chem. 2000, 72, 5239-5243.) These methodologies are combined in hybrid techniques which utilize both ESI and MALDI for sample volatilization and ionization, including MALDESI (See Sampson, J. S.; Hawkridge, A. M.; Muddiman, D. C. J. Am. Soc. Mass Spec. 2006, 17, 1712-1716.) and ELDI (See Sheia, J.; Huang, M.; Hsu, H.; Lee, C.; Yuan, C.; Beech, I.; Sunner, J. Rapid Commun. Mass Spectrom. 2005, 19, 3701-3704.).
Another category of prominent methods are electrical discharge or plasma based, and include the low temperature plasma probe, (See Harper, J. D.; Charipar, N. A.; Mulligan, C. C.; Zhang, X.; Cooks, R. G.; Ouyang, Z. Anal. Chem. 2008, 80, 9097-9104; and Zhang, Y.; Ma, X.; Zhang, S.; Yang, C.; Ouyang, Z.; Zhang, X. Analyst 2009, 134, 176-181.), direct analysis in real time (DART) (See Cody, R. B.; Laramee, J. A.; Durst, H. D. Anal. Chem. 2005, 77, 2297-2302.) and plasma-assisted desorption/ionization (PADI). (See Ratcliffe, L. V.; Rutten, F. J. M.; Barrett, D. A.; Whitmore, T.; Seymour, D.; Greenwood, C.; Aranda-Gonzalvo, Y.; Robinson, S.; McCoustra, M. Anal. Chem. 2007, 79, 6094-6101.) In just the last half decade, the field of ambient mass spectrometry has grown from just a few to nearly 40 different techniques. Excellent reviews on the subject of ambient ionization which give a comprehensive listing of the ionization sources available for both surface sampling (See Van Berkel, G. J.; Pasilis, S. P.; Ovchinnikova, O. J. Mass Spectrom. 2008, 43, 1161-1180.) and ambient (See Harris, G. A.; Nyadon, L.; Fernandez, F. M. Analyst 2008, 133, 1297-1301.) mass spectrometry as well as ion mobility spectrometry (See Guharay, S. K.; Dwivedi, P.; Hill, H. H. IEEE Trans. Plasma Sci. 2008, 36, 1458-1470.) are available.
There is a need for an efficient, small, low-power ionization source for mass spectrometry and other analytical applications.